Method of manufacturing inkjet printhead using crosslinked polymer

ABSTRACT

Provided is a method of manufacturing an inkjet printhead. The method includes: preparing a substrate having thereon a heater for heating ink and an electrode for supplying current to the heater; applying a negative photoresist composition to the substrate having thereon the heater and the electrode and patterning the same to form a passage forming layer that surrounds an ink passage; patterning the substrate having thereon the passage forming layer by photolithography at least twice to form a sacrificial layer having a planarized upper surface in a space surrounded by the passage forming layer; applying the negative photoresist composition to the passage forming layer and the sacrificial layer and patterning the same to form a nozzle layer having a nozzle; etching the substrate from the rear surface thereof to be perforated to form an ink supply hole; and removing the sacrificial layer, wherein the negative photoresist composition includes a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone. The sacrificial layer may be planarized using a chemical mechanical polishing process. Therefore, an upper surface of the sacrificial layer can be planarized, and thus, it is possible to easily control a shape and dimension of an ink passage, thereby improving uniformity of the ink passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of co-pending U.S. patent application Ser. No. 11/415,198, entitled, “METHOD OF MANUFACTURING INKJET PRINTHEAD USING CROSSLINKED POLYMER”, which was filed on May 2, 2006 and claims priority under 35 U.S.C. §119(a) from Korean Patent Application No. 2005-39712, filed on May 12, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to a method of manufacturing an inkjet printhead, and more particularly, to a method of manufacturing an inkjet resist composition printhead by photolithography using a crosslinked polymer.

2. Description of the Related Art

In general, inkjet printheads are devices for printing a predetermined color image by ejecting small droplets of printing ink at a desired position on a recording sheet. Ink ejection mechanisms of an inkjet printer are generally categorized into two different types: a thermally driven type (bubble-jet type), in which a heat source is employed to form bubbles in ink thereby causing an ink droplet to be ejected, and an piezoelectrically driven type, in which an ink droplet is ejected by a change in ink volume due to deformation of a piezoelectric element.

A typical structure of a conventional thermally-driven inkjet printhead is illustrated in FIG. 1. Referring to FIG. 1, the inkjet printhead includes a substrate 10, a passage forming layer 20 stacked on the substrate 10, and a nozzle plate 30 formed on the passage plate 20. An ink supply hole 51 is formed in the substrate 10. The passage forming layer 20 has an ink chamber 53 to store ink and a restrictor 52 connecting the ink supply hole 51 and the ink chamber 53. The nozzle layer 30 has a nozzle 54 through which the ink is ejected from the ink chamber 53. Also, the substrate 10 has a heater 41 for heating ink in the ink chamber 53 and an electrode 42 for supplying current to the heater 41.

The ink ejection mechanism of the conventional thermally-driven inkjet printhead having the above-described configuration will now be described. Ink is supplied from an ink reservoir (not illustrated) to the ink chamber 53 through the ink supply hole 51 and the restrictor 52. The ink filling the ink chamber 53 is heated by a heater 41 consisting of resistive heating elements. The ink boils to form bubbles and the bubbles expand so that the ink in the ink chamber 53 is ejected by a bubble pressure. Accordingly, the ink in the ink chamber 53 is ejected outside the ink chamber 53 through the nozzle 54 in the form of ink droplets.

The conventional thermally-driven inkjet printhead having the above-described configuration can be monolithically manufactured by photolithography, and the photolithography manufacturing process thereof is illustrated in FIGS. 2A through 2E.

Referring to FIG. 2A, a substrate 10 having a predetermined thickness is prepared, and a heater 41 for heating ink and an electrode 42 for supplying a current to the heater 41 are formed on the substrate 10.

As illustrated in FIG. 2B, a negative type photoresist composition is applied to the entire surface of the substrate 10 to a predetermined thickness and the negative type photoresist composition is then patterned in such a shape as to surround an ink chamber 53 (see FIG. 2E) and a restrictor 52 (see FIG. 2E) by photolithography, thereby forming a passage forming layer 20.

As illustrated in FIG. 2C, a space surrounded by the passage forming layer 20 is filled with a positive-type photoresist composition, thereby forming a sacrificial layer S. In detail, the positive-type photoresist composition is applied to the entire surface of the substrate 10 to a predetermined thickness and the positive-type photoresist composition is then patterned, thereby forming a sacrificial layer S. Here, the positive-type photoresist composition is generally applied by spin coating, and the top surface of the applied positive-type photoresist is not planarized (i.e., has an uneven surface, as illustrated in FIGS. 2C and 2D) due to the centrifugal force of the spin coating. In other words, the positive-type photoresist bulges upward around the passage forming layer 20 due to the centrifugal force provided during spin coating, as indicated by the double-dashed line illustrated in FIG. 2C. If the uneven surface of the positive-type photoresist is patterned, the sacrificial layer S protrudes upward at its peripheral edges, as illustrated in FIG. 2D.

As illustrated in FIG. 2D, a negative type photoresist composition is applied to the passage forming layer 20 and the sacrificial layer S to a predetermined thickness and the negative type photoresist composition is then patterned by photolithography, thereby forming a nozzle layer 30 having a nozzle 54.

Subsequently, as illustrated in FIG. 2E, the bottom surface of the substrate 10 is wet-etched to form an ink supply hole 51, and the sacrificial layer S is removed through the ink supply hole 51, thereby forming the restrictor 52 and the ink chamber 53 in the passage forming layer 20.

Referring back to FIG. 2D, when forming the nozzle layer 30 by applying a crosslinked polymer resist composition to the sacrificial layer S, a projecting edge of the sacrificial layer S made of the positive-type photoresist may react with a solvent contained in the crosslinked polymer resist composition, causing deformation or melting. Then, as illustrated in FIG. 2E, a cavity C is formed between the passage forming layer 20 and the nozzle layer 30. Furthermore, the passage forming layer 20 and the nozzle layer 30 are not suitably adhered to each other due to existence of the cavity C formed between the passage forming layer 20 and the nozzle layer 30.

As described above, according to the conventional manufacturing method of an inkjet printhead, since the shape and dimension of an ink passage are not easily controlled, it is difficult to attain uniformity of the ink passage, and an ink ejection performance of the printhead may deteriorate. Further, since the passage forming layer 20 and the nozzle layer 30 are not suitably adhered to each other, the durability of the inkjet printhead is lowered.

Referring back to FIG. 2D, the crosslinked polymer resist composition applied to the sacrificial layer S is patterned by exposure, development, and baking. During the exposure, broadband UV light, including I-line (353 nm), H-line (405 nm), and G-line (436 nm), is usually used. Here, the H-line and the G-line, each having a relatively long wavelength and a long penetration depth, affect both the crosslinked polymer resist composition forming the nozzle layer 30 and the positive photoresist forming the sacrificial layer S disposed under the nozzle layer 30. Also, when the positive photoresist is irradiated with UV light, a photosensitizer contained therein may be decomposed by the light, producing nitrogen (N₂) gas. The produced nitrogen gas expands during baking to lift the nozzle layer 30, resulting in deformation of the nozzle layer 30.

SUMMARY OF THE INVENTION

The present general inventive concept provides a method of manufacturing an inkjet printhead that can easily control a shape and dimension of an ink passage by planarizing a top surface of a sacrificial layer, thereby improving uniformity of the ink passage, and an inkjet printhead manufactured by the method.

The present general inventive concept provides an inkjet printhead having a planarized surface of a sacrificial layer to control a shape and a dimension of an ink passage, thereby improving uniformity of the ink passage and preventing deformation of a nozzle layer due to gas generated in the sacrificial layer.

Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing a method of manufacturing an inkjet printhead, the method including: preparing a substrate having thereon a heater for heating ink and an electrode for supplying current to the heater; applying a negative photoresist composition to the substrate having thereon the heater and the electrode and patterning the negative photoresist composition to form a passage forming layer that surrounds an ink passage; patterning the substrate having thereon the passage forming layer by photolithography at least twice to form a sacrificial layer having a planarized upper surface in a space surrounded by the passage forming layer; applying the negative photoresist composition to the passage forming layer and the sacrificial layer and patterning the negative photoresist composition to form a nozzle layer having a nozzle; etching a rear surface of the substrate to form an ink supply hole; and removing the sacrificial layer, wherein the negative photoresist composition includes a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The monomers in the prepolymer can all have an identical formula. The monomers in the prepolymer can all have different formulas. The monomers in the prepolymer can include a mixture of some of the monomers having an identical formula and others of the monomers having different formulas.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an inkjet printhead manufactured by the method.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of manufacturing an inkjet printhead, the method including: applying a first negative photoresist composition to a substrate having thereon a heater and an electrode; patterning the first negative photoresist composition to form a passage forming layer that surrounds an ink passage; patterning the substrate having thereon the passage forming layer by photolithography at least twice to form a sacrificial layer having a planarized upper surface in a space surrounded by the passage forming layer; applying a second negative photoresist composition including a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone to the passage forming layer and the sacrificial layer; patterning the second negative photoresist composition to form a nozzle layer having a nozzle; and removing the sacrificial layer.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of manufacturing an inkjet printhead, the method including: applying to a substrate a negative photoresist composition including a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone; exposing the negative photoresist composition applied to the substrate to ultraviolet light to form a first crosslinked polymer; developing the first crosslinked polymer; applying a positive photoresist composition to the substrate and the first crosslinked polymer; exposing the positive photoresist composition applied to the substrate and the first crosslinked polymer to ultraviolet light to form a first sacrificial layer; developing the first sacrificial layer; applying the positive photoresist composition to the substrate, the first crosslinked polymer, and the first sacrificial layer; exposing the positive photoresist composition applied to the substrate, the first crosslinked polymer, and the first sacrificial layer to ultraviolet light to form a second sacrificial layer having a planarized upper surface; and developing the second sacrificial layer.

The exposing of the negative photoresist composition applied to the substrate may include exposing the negative photoresist composition through a first photomask having a passage forming layer pattern to ultraviolet light to form the first crosslinked polymer. The exposing of the positive photoresist composition applied to the substrate and the first crosslinked polymer may include exposing the positive photoresist composition through a second photomask having an ink chamber pattern to ultraviolet light to form the first sacrificial layer. The exposing of the positive photoresist composition applied to the substrate, the first crosslinked polymer, and the first sacrificial layer may include exposing the positive photoresist composition through a second photomask having an ink chamber pattern to ultraviolet light to form the second sacrificial layer having a planarized upper surface.

The method may further include repeatedly blank exposing the second sacrificial layer having the planarized upper surface until a height of the second sacrificial layer is substantially equal to a height of the passage forming layer, developing the blank exposed second sacrificial layer, applying a negative photoresist composition including a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone to the substrate and the second sacrificial layer, exposing the negative photoresist composition applied to the substrate and the second sacrificial layer to ultraviolet light to form a second crosslinked polymer, and developing the second crosslinked polymer. The exposing of the negative photoresist composition applied to the substrate and the second sacrificial layer may include exposing the negative photoresist composition through a third photomask having a nozzle layer pattern to ultraviolet light to form the second crosslinked polymer. The method may further include applying a negative photoresist composition including a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic backbone to the substrate and the second sacrificial layer, exposing the negative photoresist composition applied to the substrate and the second sacrificial layer to ultraviolet light to form a second crosslinked polymer, and developing the second crosslinked polymer, in which the positive photoresist composition is an imide-based positive photoresist composition. The exposing of the negative photoresist composition applied to the substrate and the second sacrificial layer can include exposing the negative photoresist composition through a third photomask having a nozzle layer pattern to ultraviolet light to form the second crosslinked polymer.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a photolithography method, including applying a first negative photoresist composition to a substrate having a heater and an electrode formed thereon, patterning the negative photoresist composition to form a passage forming layer, applying a positive photoresist composition to a location on the substrate surrounded by the passage forming layer, patterning the positive photoresist composition to form a sacrificial layer, applying a second negative photoresist composition including a prepolymer that a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone to the passage forming layer and the sacrificial layer, patterning the second negative photoresist composition to form a nozzle having a nozzle layer, and removing the sacrificial layer. The first negative photoresist composition may include a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone. The positive photoresist composition can be an imide-based positive photoresist composition.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an inkjet printhead including: a substrate having thereon at least one heater and at least one electrode and having an ink passage; a passage forming layer, disposed on the substrate, defining an ink chamber; and a nozzle layer, disposed on the passage forming layer, including a crosslinked product of a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

A height of the ink chamber can be substantially equal to a height of the passage forming layer. A height of the ink chamber can be greater than a height of the passage forming layer. The passage forming layer can include a crosslinked product of a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an inkjet printhead intermediate useable to make an inkjet printhead, including: a substrate having thereon at least one heater and at least one electrode and having an ink passage; and a first crosslinked polymer resist layer, disposed on the substrate, including a crosslinked product of a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenol novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an inkjet printhead intermediate useable to make an inkjet printhead, including: a substrate having thereon at least one heater and at least one electrode and having an ink passage; a passage forming layer, disposed on the substrate, defining an ink chamber; and a sacrificial layer having a planarized upper surface disposed on a portion of the substrate substantially surrounded by the passage forming layer.

The passage forming layer can include a crosslinked product of a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone. The sacrificial layer can include an imide-based positive photoresist composition. A height of the sacrificial layer can be substantially equal to a height of the passage forming layer. A height of the sacrificial layer can be greater than a height of the passage forming layer. The inkjet printhead intermediate can further include a polymer layer, disposed on the sacrificial layer, including a crosslinked product of a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an inkjet printhead including: a substrate having a passage, at least one heater formed on a first portion of the substrate, at least one electrode formed on a second portion of the substrate, a passage forming layer formed on a third portion of the substrate, and a nozzle layer formed on the passage forming layer, having a planarized surface facing the substrate. The surface of the nozzle layer and a surface of the passage forming layer can form an angle without a cavity on at least one of the surfaces of the nozzle layer and the passage forming layer.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of manufacturing an inkjet printhead, including forming a substrate having a passage, forming at least one heater on a first portion of the substrate, forming at least one electrode on a second portion of the substrate, forming a passage forming layer on a third portion of the substrate, and forming a nozzle layer having a planarized surface facing the substrate on the passage forming layer. The forming of the nozzle layer having the planarized surface facing the substrate on the passage forming layer can include forming an angle without a cavity between the surface of the nozzle layer and a surface of the passage forming layer.

The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of manufacturing an inkjet printhead, the method including: preparing a substrate having thereon a heater for heating ink and an electrode for supplying current to the heater; coating a negative photoresist composition on the substrate having thereon the heater and the electrode and patterning the negative photoresist composition using a photolithography process to form a passage forming layer that defines an ink passage; forming a sacrificial layer on the substrate having thereon the passage forming layer so as to cover the passage forming layer; planarizing upper surfaces of the passage forming layer and the sacrificial layer using a polishing process; coating a negative photoresist composition on the passage forming layer and the sacrificial layer and patterning the negative photoresist composition using a photolithography process to form a nozzle layer having a nozzle; forming an ink feed hole in the substrate; and removing the sacrificial layer, wherein the negative photoresist composition includes a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The polishing process may be a chemical mechanical polishing (CMP) process. The substrate may be a silicon wafer.

According to the present invention, an upper surface of a sacrificial layer can be planarized, and thus, it is possible to easily control the shape and dimension of an ink passage, thereby improving uniformity of the ink passage. Moreover, no gas is generated in the sacrificial layer, thereby avoiding deformation of a nozzle layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic perspective view illustrating a structure of a conventional thermally-driven inkjet printhead;

FIGS. 2A through 2E are cross-sectional views illustrating a method of manufacturing the conventional inkjet printhead illustrated in FIG. 1;

FIGS. 3A through 3R are cross-sectional views illustrating a method of manufacturing an inkjet printhead according to an embodiment of the present general inventive concept;

FIGS. 4A through 4F are cross-sectional views illustrating a method of manufacturing inkjet printhead according to an embodiment of the present general inventive concept; and

FIG. 5A is a vertical cross-sectional view of an inkjet printhead according to an embodiment of the present general inventive concept, and FIG. 5B is an enlarged view illustrating the vertical cross-sectional view in FIG. 5A;

FIGS. 6A through 6L are sectional views illustrating a method of manufacturing an inkjet printhead according to an embodiment of the present invention;

FIGS. 7A and 7B are images showing a passage forming layer and a sacrificial layer after a chemical mechanical polishing (CMP) process in a method of manufacturing an inkjet printhead according to an embodiment of the present invention; and

FIGS. 8A and 8B are vertical sectional views illustrating an inkjet printhead manufactured by a method of manufacturing an inkjet printhead according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Korean Patent Application No. 2005-39712, filed on May 12, 2005, in the Korean Intellectual Property Office, and entitled: “METHOD OF MANUFACTURING INKJET PRINTHEAD USING CROSSLINKED POLYMER” is incorporated by reference herein in their entirety.

Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.

The present general inventive concept provides a method of manufacturing an inkjet printhead, the method including: preparing a substrate having thereon a heater for heating ink and an electrode for supplying current to the heater; applying a negative photoresist composition to the substrate having thereon the heater and the electrode and patterning the negative photoresist composition to form a passage forming layer that surrounds an ink passage; patterning the substrate having thereon the passage forming layer by photolithography at least twice to form a sacrificial layer having a planarized upper surface in a space surrounded by the passage forming layer; applying the negative photoresist composition to the passage forming layer and the sacrificial layer and patterning the negative photoresist composition to form a nozzle layer having a nozzle; etching a rear surface of the substrate to form an ink supply hole; and removing the sacrificial layer, wherein the negative photoresist composition includes a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group (hereinafter, referred to as simply “glycidyl ether functional group”) on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

In embodiments, the negative photoresist composition may include the prepolymer, a cationic photoinitiator, and a solvent.

The prepolymer of the negative photoresist composition may form a crosslinked polymer by exposing the prepolymer to an actinic radiation.

The prepolymer may be prepared from a backbone monomer unit selected from the group consisting of phenol, o-cresol, p-cresol, bisphenol-A, an alicyclic compound, and mixtures thereof.

The prepolymer may include at least one represented by Formulas 1-7 below:

In each of the above structural Formulas 1-7, m is an integer ranging from 1 to 20, and n is an integer ranging from 1 to 20. The prepolymer may also be addition products of 1-2-epoxy-4(2-oxiranyl)-cyclohexane of 2,2-bis(hydroxy methyl)-1-butanol (which are commercially available under the trade name of EHPH-3150).

The cationic photoinitiator can be, for example, a sulfonium salt or an iodonium salt.

The solvent may be at least one compound selected from the group consisting of

-butyrolactone, propylene glycol methyl ether acetate (PGMEA), tetrahydrofuran (THF), methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and mixtures thereof.

According to an embodiment of the present general inventive concept, an inkjet printhead can be manufactured by a method including applying a first crosslinked polymer resist composition to a substrate having a heater and an electrode and patterning the first crosslinked polymer resist composition to form a passage forming layer that surrounds an ink passage, patterning the substrate having the passage forming layer by photolithography at least twice, forming a sacrificial layer having a planarized upper surface in a space surrounded by the passage forming layer, applying a second crosslinked polymer resist composition to the passage forming layer and the sacrificial layer and patterning the second crosslinked polymer resist composition to form a nozzle layer having a nozzle, and removing the sacrificial layer.

In embodiments, a step difference between a chamber layer of the inkjet printhead and the sacrificial layer is not greater than about 3 μm.

Monomers forming the prepolymer can all have an identical formula. The monomers forming the prepolymer can all have different formulas. The monomers forming the prepolymer can include a mixture of some of monomers having an identical formula and others of monomers having different formulae.

The present general inventive concept also provides a method of manufacturing an inkjet printhead, the method including: applying to a substrate a negative photoresist composition including a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone; exposing the negative photoresist composition applied to the substrate to ultraviolet (UV) light to form a first crosslinked polymer; developing the first crosslinked polymer; applying a positive photoresist composition to the substrate and the first crosslinked polymer; exposing the positive photoresist composition applied to the substrate and the first crosslinked polymer to UV light to form a first sacrificial layer; developing the first sacrificial layer; applying the positive photoresist composition to the substrate, the first crosslinked polymer, the first sacrificial layer; exposing the positive photoresist composition applied to the substrate, the first crosslinked polymer, and the first sacrificial layer to UV light to form a second sacrificial layer having a planarized upper surface; and developing the second sacrificial layer.

The exposing of the negative photoresist composition applied to the substrate may include exposing the negative photoresist composition to UV light using a first photomask having a passage forming layer pattern to form the first crosslinked polymer.

The exposing of the positive photoresist composition applied to the substrate and the first crosslinked polymer may include exposing the positive photoresist composition to UV light using a second photomask having an ink chamber pattern to form the first sacrificial layer.

The exposing of the positive photoresist composition applied to the substrate, the first crosslinked polymer, and the first sacrificial layer may include exposing the positive photoresist composition to UV light using a second photomask having an ink chamber pattern to form the second sacrificial layer having a planarized upper surface.

The method may further include repeatedly blank exposing the second sacrificial layer having the planarized upper surface until a height of the second sacrificial layer is substantially equal to a height of the passage forming layer; developing the blank exposed second sacrificial layer; applying a negative photoresist composition including a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone to the substrate and the second sacrificial layer; exposing the negative photoresist composition applied to the substrate and the second sacrificial layer to UV light to form a second crosslinked polymer; and developing the second crosslinked polymer.

The exposing of the negative photoresist composition applied to the substrate and the second sacrificial layer may include exposing the negative photoresist composition to UV light using a third photomask having a nozzle layer pattern to form the second crosslinked polymer.

The method may further include applying a negative photoresist composition including a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone to the substrate and the second sacrificial layer; exposing the negative photoresist composition applied to the substrate and the second sacrificial layer to UV light to form a second crosslinked polymer; and developing the second crosslinked polymer, wherein the positive photoresist composition is an imide-based positive photoresist composition.

The exposing of the negative photoresist composition applied to the substrate and the second sacrificial layer can include exposing the negative photoresist composition to UV light using a third photomask having a nozzle layer pattern to form the second crosslinked polymer.

The present general inventive concept also provides an inkjet printhead including: a substrate having thereon at least one heater and at least one electrode and having an ink passage; a passage forming layer, disposed on the substrate, defining an ink chamber; and a nozzle layer, disposed on the passage forming layer, including a crosslinked product of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

A height of the ink chamber can be substantially equal to a height of the passage forming layer. A height of the ink chamber can be greater than a height of the passage forming layer. The passage forming layer can include a crosslinked product of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The present general inventive concept also provides an inkjet printhead intermediate useable to make an inkjet printhead, including: a substrate having thereon at least one heater and at least one electrode and having an ink passage; and a first polymer layer, disposed on the substrate, including a crosslinked product of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The present general inventive concept also provides an inkjet printhead intermediate useable to make an inkjet printhead, including: a substrate having thereon at least one heater and at least one electrode and having an ink passage; a passage forming layer, disposed on the substrate, defining an ink chamber; and a sacrificial layer having a planarized upper surface disposed on a portion of the substrate substantially surrounded by the passage forming layer.

The passage forming layer may include a crosslinked product of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The sacrificial layer may include an imide-based positive photoresist composition. A height of the sacrificial layer may be substantially equal to a height of the passage forming layer. A height of the sacrificial layer may be greater than a height of the passage forming layer.

The inkjet printhead intermediate may further include a polymer layer, disposed on the sacrificial layer, including a crosslinked product of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.

The present general inventive concept also provides a method of manufacturing an inkjet printhead, the method including: preparing a substrate having thereon a heater for heating ink and an electrode for supplying current to the heater; coating a negative photoresist composition on the substrate having thereon the heater and the electrode and patterning the negative photoresist composition using a photolithography process to form a passage forming layer that defines an ink passage; forming a sacrificial layer on the substrate having thereon the passage forming layer so as to cover the passage forming layer; planarizing upper surfaces of the passage forming layer and the sacrificial layer using a polishing process; coating the negative photoresist composition on the passage forming layer and the sacrificial layer and patterning the negative photoresist composition using a photolithography process to form a nozzle layer having a nozzle; forming an ink feed hole in the substrate; and removing the sacrificial layer, wherein the negative photoresist composition includes a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone

The polishing process may be a chemical mechanical polishing (CMP) process. The substrate may be a silicon wafer.

The formation of the passage forming layer may include forming a first photoresist layer by coating the negative photoresist composition on the entire surface of the substrate; exposing the first photoresist layer using a first photomask having an ink passage pattern; and forming the passage forming layer by developing the first photoresist layer to remove an unexposed portion of the first photoresist layer.

The sacrificial layer may include a positive photoresist or a non-photosensitive soluble polymer. The positive photoresist may be an imide-based positive photoresist. The non-photosensitive soluble polymer may be at least one selected from the group consisting of a phenolic resin, a polyurethane resin, an epoxy resin, a polyimide resin, an acrylic resin, a polyamide resin, an urea resin, a melamine resin, and a silicone resin. Here, the term “soluble” refers to characteristics that can be dissolved in a solvent.

In the formation of the sacrificial layer, the sacrificial layer may be formed to be higher than the passage forming layer. Here, the sacrificial layer may be formed using a spin coating process.

In the planarization of the upper surfaces of the passage forming layer and the sacrificial layer, the upper surfaces of the passage forming layer and the sacrificial layer may be polished using a polishing process such as a chemical mechanical polishing process to reach a desired height of the ink passage.

The formation of the nozzle layer may include forming a second photoresist layer by coating the negative photoresist composition on the passage forming layer and the sacrificial layer; exposing the second photoresist layer using a second photomask having a nozzle pattern; and forming the nozzle layer having the nozzle by developing the second photoresist layer to remove an unexposed portion of the second photoresist layer.

The formation of the ink feed hole may include coating a photoresist on a rear surface of the substrate; forming an etch mask for forming the ink feed hole by patterning the photoresist; and etching a rear surface portion of the substrate exposed through the etch mask to form the ink feed hole. Here, the rear surface of the substrate may be etched by a dry etching process using plasma or a wet etching process using tetramethylammonium hydroxide (TMAH) or KOH as an etchant.

The negative photoresist composition may further include a cationic photoinitiator and a solvent, in addition to the prepolymer having the glycidyl ether functional group. The prepolymer having the glycidyl ether functional group may be prepared from a backbone monomer unit selected from the group consisting of phenol, o-cresol, p-cresol, bisphenol-A, an alicyclic-based compound, and mixtures thereof.

The prepolymer having the glycidyl ether functional group may include at least one represented by Formulas 1-7 above. The prepolymer may also be addition products of 1-2-epoxy-4(2-oxiranyl)-cyclohexane of 2,2-bis(hydroxy methyl)-1-butanol (which are commercially available under the trade name of EHPH-3150).

The prepolymer having the glycidyl ether functional group in the negative photoresist composition may be crosslinked by exposure to radiation of actinic ray, e.g., UV light.

The cationic photoinitiator may be a sulfonium salt or an iodonium salt.

The solvent may be at least one selected from the group consisting of

-butyrolactone, propylene glycol methyl ether acetate (PGMEA), tetrahydrofuran (THF), methyl ethyl ketone, methy isobutyl ketone, cyclopentanone, and mixtures thereof.

According to the present invention, an upper surface of a sacrificial layer can be planarized, and thus, it is possible to easily control the shape and dimension of an ink passage, thereby improving uniformity of the ink passage. A crosslinked polymer constituting a chamber and a nozzle layer according to the present invention is prepared by crosslinking of a prepolymer that has a plurality of glycidyl ether functional groups and a phenolic novolak resin-based backbone, a bisphenol-A backbone, or an alicyclic-based backbone. Generally, the glycidyl ether functional groups can be disposed on hydrogen positions of phenolic hydroxy groups.

A difunctional epoxy resin having two glycidyl ether groups may be represented by Formula 7 below:

wherein m is an integer ranging from 1 to 25, preferably an integer of 1 to 20.

The difunctional epoxy resin having two glycidyl ether groups can form a film with a low crosslinking density.

The content of the difunctional epoxy resin may range from about 5 to about 50% by weight, preferably from about 10 to about 20% by weight, based on the total weight of the negative photoresist composition.

Examples of the difunctional epoxy resin having two glycidyl ether groups include, but are not limited to, EPON 828, EPON 1004, EPON 1001F, and EPON 1010 (which are commercially obtainable from Shell Chemicals), DER-332, DER-331, and DER-164 (which are commercially obtainable from Dow Chemical Company), and ERL-4201 and ERL-4289 (which are commercially obtainable from Union Carbide Corporation).

A multifunctional epoxy resin having more than two glycidyl ether groups will now be described.

The multifunctional epoxy resin having more than two glycidyl ether group can form a film with a high crosslinking density, increasing a resolution and thereby preventing swelling with respect to ink or a solvent. The content of the multifunctional epoxy resin may range from about 0.5 to about 20% by weight, preferably from about 1 to about 5% by weight, based on the total weight of the negative photoresist composition.

Examples of the multifunctional epoxy resin having more than two glycidyl ether groups include, but are not limited to, EPON SU-8 and EPON DPS-164 (which are commercially obtainable from Shell Chemicals), DEN-431 and DEN-439 (which are commercially obtainable from Dow Chemical Company), and EHPE-3150 (which is commercially obtainable from Daicel Chemical Industries, Ltd.).

Examples of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone include compounds represented by Formula 1 below:

The prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone may also use o-cresol or p-cresol instead of phenol when designing a backbone structure, as represented by Formulas 2 and 3 below:

Examples of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a bisphenol-A-based backbone include compounds represented by Formulas 5 and 6 below:

The number n of the monomer repeating units can range from 1 to about 20, preferably from 1 to about 10.

Examples of a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and an alicyclic-based backbone include addition products of 1-2-epoxy-4(2-oxiranyl)-cyclohexane of 2,2-bis(hydroxy methyl)1-butanol (which are commercially available under the trade name of EHPH-3150).

Photoinitiators are compounds that can generate ions or free radicals that initiate polymerization upon exposure to light. The content of the photoinitiator may range from about 1.0 to about 10% by weight, preferably from about 1.5 to 5% by weight, based on the total weight of the negative photoresist composition. If the content of the photoinitiator is less than 1.0% by weight, unreacted prepolymers may be left due to insufficient photopolymerization. On the other hand, if the content of the photoinitiator exceeds 10% by weight, energy higher than the energy value corresponding to a film thickness may be needed, and the wall profile of a pattern may be changed.

Examples of suitable photoinitiators include, but are not limited to, aromatic halominum salts and aromatic onium salts of Group VA or VI elements. For example, suitable photoinitiators include, but are not limited to, UVI-6974 (which is commercially obtainable from Union Carbide Corporation), SP-172 (which is commercially obtainable from Asahi denka, Co., Ltd.), and on the like.

Specific examples of the aromatic sulfonium salt include, but are not limited to, triphenylsulfonium tetrafluoroborate, triphenylsulfonium hexafluoroantimonate (UVI-6974), phenylmethylbenzylsulfonium hexafluoroantimonate, phenylmethylbenzylsulfonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, methyl diphenylsulfonium tetrafluoroborate, and dimethyl phenylsulfonium hexafluorophsophate.

Specific examples of the aromatic iodonium salt include, but are not limited to, diphenyliodonium tetrafluoroborate, diphenyliodonium hexafluoroantimonate, and butylphenyl iodonium hexafluoroantimonate (SP-172).

Examples of suitable solvents include, but are not limited to,

-butyrolactone, propylene glycol methyl ether acetate (PGMEA), tetrahydrofuran (THF), methyl ethyl ketone, methy isobutyl ketone, and mixtures thereof. A suitable content of the solvent can range from about 20 to about 90% by weight, preferably from about 45 to 75% by weight, based on the total weight of the negative photoresist composition.

As additional additives, photosensitizers, silane coupling agents, fillers, viscosity modifiers, and the like, can be used.

Sensitizers absorb light energy and facilitate the transfer of energy to another compound, which can then form radical or ionic initiators. Sensitizers frequently expand a useful energy wavelength range for photoexposure, and typically are aromatic light absorbing chromophores. Sensitizers can also lead to the formation of photoinitiators, which can be free radical or ionic forms.

When present, the sensitizer can be present in an amount of from about 0.1 to about 20% by weight based on the total weight of the negative photoresist composition.

FIGS. 3A through 3R are cross-sectional views illustrating a method of manufacturing an inkjet printhead using a prepolymer that has a glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol-A-based backbone, or an alicyclic-based backbone according to an embodiment of the present general inventive concept.

As illustrated in FIG. 3A, a heater 141 to heat ink and an electrode 142 to supply current to the heater 141 can be formed on a substrate 110.

A silicon wafer is used as the substrate 110 in FIGS. 3A-3R. A silicon wafer is widely used in manufacturing semiconductor devices and is advantageous for mass production. However, the present general inventive concept is not limited to the substrate 110 being a silicon wafer.

The heater 141 can be formed by depositing a resistive heating element, such as tantalum-nitride or a tantalum-aluminum alloy, on the substrate 110 by sputtering or chemical vapor deposition (CVD) and patterning the deposited resistive heating element. The electrode 142 can be formed by depositing a metal having good conductivity, such as aluminum or an aluminum alloy, on the substrate 110 by sputtering and patterning the deposited metal. Although not illustrated, a passivation layer made of, for example, silicon oxide or silicon nitride, may be formed on the heater 141 and the electrode 142.

As illustrated in FIG. 3B, a first negative photoresist layer 121 can be formed on the substrate 110 where the heater 141 and the electrode 142 are formed. The first negative photoresist layer 121 forms a passage forming layer (see 120 of FIG. 3D) surrounding an ink chamber and a restrictor, which will be described later. In particular, the first negative photoresist layer 121 can be formed by applying a negative photoresist composition containing a prepolymer having a glycidyl ether functional group to a predetermined thickness to an entire surface of the substrate 110. The negative photoresist composition is as described above. Here, the negative photoresist composition may be applied to a thickness substantially corresponding to a height of the ink chamber so as to accommodate the quantity of ink droplets ejected. The negative photoresist composition may be applied to the substrate 110 using a spin coating process.

As illustrated in FIG. 3C, the first negative photoresist layer 121 can be exposed to an actinic radiation, such as UV light, using a first photomask 161 having a passage forming layer pattern. Specifically, an exposed portion of the first negative photoresist layer 121 can be cured so as to have chemical resistance and high mechanical strength. On the other hand, an unexposed portion of the first negative photoresist layer 121 is easily dissolved in a developer.

Then, when the first negative photoresist layer 121 is developed, the unexposed portion is removed to form a space, and the exposed and cured portion is left to form a passage forming layer 120, as illustrated in FIG. 3D.

FIGS. 3E through 3L illustrate the formation of a sacrificial layer S in the space surrounded by the passage forming layer 120. The sacrificial layer S has a planarized upper surface (i.e., the upper surface does not protrude at its peripheral edges, and does not bulge upward around the passage forming layer 120). According to various embodiments of the present general inventive concept, the upper surface of the sacrifical layer S can be planarized by applying a positive photoresist, patterning the positive photoresist at least twice, and planarizing the resulting structure once.

In more detail, as illustrated in FIG. 3E, the positive photoresist can be applied to the entire surface of the substrate 110 having thereon the passage forming layer 120 to a predetermined thickness by spin-coating, thereby forming a first sacrificial layer 123. Here, the positive photoresist bulges upward due to the protruding passage forming layer 120, making the upper surface of the first sacrificial layer 123 uneven. As illustrated in FIG. 3F, the first sacrificial layer 123 can be exposed to UV light using a second photomask 162 having a predetermined pattern covering a region between patterns of the passage forming layer 120. Specifically, a portion of the first sacrificial layer 123 exposed to UV light becomes easily dissolved in a developer. Thus, when the first sacrificial layer 123 is developed, only an unexposed portion of the first sacrificial layer 123 is left while the exposed portion is removed, as illustrated in FIG. 3G.

As illustrated in FIG. 3H, a positive photoresist is applied for a second time to the entire surface of the substrate 110 having thereon the passage forming layer 120 and the first sacrificial layer 123 to a predetermined thickness by spin-coating, thereby forming a second sacrificial layer 124. The upper surface of the second sacrificial layer 124 can be planarized by the first sacrificial layer 123 filled in the space surrounded by the passage forming layer 120.

As illustrated in FIG. 3I, the second sacrificial layer 124 can be exposed to UV light using a second photomask 162, which is identical to the first photomask 162 used to expose the first sacrificial layer 123. Subsequently, the second sacrificial layer 124 can be developed to remove an exposed portion of the second sacrificial layer 124. As a result, as illustrated in FIG. 3J, the sacrificial layer S consisting of the first sacrificial layer 123 and the second sacrificial layer 124 and having the planarized upper surface can be formed in a space surrounded by the passage forming layer 120.

As illustrated in FIG. 3K, the sacrificial layer S can be exposed to UV light. Here, the exposing may be performed by blank exposure without using a photomask. The sacrificial layer S can be continuously exposed so that the upper surface of the sacrificial layer S becomes substantially the same height as that of the passage forming layer 120 by controlling an exposure time and light intensity. Next, the sacrificial layer S can be developed to remove the exposed portion of the sacrificial layer S and to lower the height of the sacrificial layer S, so that the sacrificial layer S has substantially the same height as the passage forming layer 120, as illustrated in FIG. 3L.

While the foregoing description has described that the sacrificial layer S can be formed by applying, exposing, and developing the first sacrificial layer 123 (see FIGS. 3E-3G), applying, exposing, and developing the second sacrificial layer 124 (see FIGS. 3H-3J), and then performing blank exposure and development (see FIGS. 3K-3L), the sacrificial layer S may be formed differently from the above-described formation. For example, after applying, exposing, and developing the first sacrificial layer 123 (see FIGS. 3E-3G), the application of the second sacrificial layer 124 may be followed by performing blank exposure (as opposed to the exposure through the second photomask 162 illustrated in FIG. 3I). Subsequently, development can be performed to allow the second sacrificial layer 124 and the first sacrificial layer 123 to remain as high as the passage forming layer 120. Next, the same exposure using the second photomask 162 and development steps can be performed, leaving only the sacrificial layer S surrounded by the passage forming layer 120.

Alternatively, the sacrificial layer S may be formed as described below. After applying, exposing, and developing the first sacrificial layer 123 (see FIGS. 3E-3G), the second sacrificial layer 124 can be applied and exposed using the second photomask 162 and using blank exposure. Here, the sequence of exposing using the second photomask 162 and using blank exposure may be reversed. That is, the applied second sacrificial layer 124 can be exposed using blank exposure followed by exposure using the second photomask 162. Subsequently, the exposed portion is removed by development, so that only the sacrificial layer S surrounded by the passage forming layer 120 remains.

While the foregoing description has described that the positive photoresist is applied twice in order to form a sacrificial layer S having a planarized upper surface, the positive photoresist may be applied three or more times until the sacrificial layer S has a desired thickness. In this case, the number of times of performing exposure and development increases according to the number of times of applying positive photoresist.

Next, as illustrated in FIG. 3M, a second negative photoresist layer 131 can be formed on the substrate 110 where the passage forming layer 120 and the sacrificial layer S are formed. Since the second negative photoresist layer 131 forms a nozzle layer (see 130 FIG. 3O), which will be described later, the second negative photoresist layer 131 can be formed of a material that is chemically stable against ink, like the passage forming layer 120. For this, the second negative photoresist layer 131 can be formed by applying a composition containing a prepolymer having a glycidyl ether functional group to an entire surface of the substrate 110 to a predetermined thickness by spin coating. Here, the composition containing the prepolymer having the glycidyl ether functional group may be applied to a thickness enough to obtain a sufficiently long nozzle and to withstand a change in the pressure of the ink chamber upon formation of the second negative photoresist layer 131.

Since the sacrificial layer S is formed to have substantially the same height as the passage forming layer 120, that is, the upper surface of the sacrificial layer S is planarized, it is possible to overcome the deformation or melting problem that occurs in the prior art, as discussed above. In particular, the deformation or melting of edges of the sacrificial layer S due to a reaction between the positive photoresist forming the sacrificial layer S and the material forming the second negative photoresist layer 131 that occurs in the prior art is avoided. Thus, the second negative photoresist layer 131 can be suitably adhered to the passage forming layer 120.

As illustrated in FIG. 3N, the second negative photoresist layer 131 is exposed using a third photomask 163 having a nozzle pattern. Subsequently, when the second negative photoresist layer 131 is developed, the unexposed portion is removed to form a nozzle 154, and the exposed and cured portion is left to form a nozzle layer 130, as illustrated in FIG. 3O. Actinic radiation can be used to expose the second negative photoresist layer 131. Specifically, a UV beam of not longer than an I-line radiation (353 nm), H-line radiation (405 nm), and G-line radiation (436 nm), or an e-beam or X-ray having wavelengths shorter than an I-line radiation can be used.

As described above, exposing by using light having a relatively short wavelength shortens a transmission length of light, so that the sacrificial layer S disposed under the second negative photoresist layer 131 is not affected by exposure. Thus, nitrogen gas is not generated in the sacrificial layer S formed of the positive photoresist, thereby avoiding deformation of the nozzle layer 130 due to nitrogen gas.

As illustrated in FIG. 3P, an etch mask 171 to form an ink supply hole 151 (see FIG. 3Q) can be formed on a rear surface of the substrate 110. The etch mask 171 is formed by applying a positive or negative photoresist to the rear surface of the substrate 110 and patterning the same.

Next, as illustrated in FIG. 3Q, the substrate 110 exposed by the etch mask 171 can be etched from the rear surface thereof to be perforated, thereby forming an ink supply hole 151, followed by removing the etch mask 171. More specifically, the etching of the rear surface of the substrate 110 may be performed by dry etching using, for example, plasma. Alternatively, the rear surface of the substrate 110 may be etched by wet etching using, for example, tetramethylammonium hydroxide (TMAH) or KOH as an etchant.

Finally, the sacrificial layer S can be removed using a solvent, thereby forming an ink chamber 153 and a restrictor 152 surrounded by the passage forming layer 120 in a space without the sacrificial layer S, as illustrated in FIG. 3R.

In such a manner, an inkjet printhead having the structure illustrated in FIG. 3R is completed. In embodiments, a step difference between the ink chamber 153 of the inkjet printhead and the sacrificial layer S is not greater than 3 μm.

FIGS. 4A through 4F are cross-sectional views illustrating a method of manufacturing an inkjet printhead according to another embodiment of the present general inventive concept. In the following description, the same portions as those described above with respect to the embodiment illustrated in FIGS. 3A-3N will be briefly described or omitted for the sake of brevity.

A sacrificial layer S is formed on a substrate 210 in substantially the same manner as illustrated in FIGS. 3A through 3J, which will now be described briefly. As illustrated in FIG. 4A, the substrate 210 is prepared and a heater 241 to heat ink and an electrode 242 to supply current to the heater 241 are formed on the substrate 210. Next, a negative photoresist composition containing a prepolymer having a glycidyl ether functional group is applied to the substrate 210 having thereon the heater 241 and the electrode 242 to a predetermined thickness, followed by exposing and developing the negative photoresist composition, thereby forming a passage forming layer 220 which is a first negative photoresist layer. At this time, the passage forming layer 220 may be formed to be slightly lower than an ink chamber having a desired height. Then, a positive photoresist composition is applied to an entire surface of the substrate 210 having thereon the passage forming layer 220 to a predetermined thickness by spin-coating, thereby forming a first sacrificial layer 223, and the applied positive photoresist composition is exposed and developed. Subsequently, the positive photoresist composition is applied a second time to the entire surface of the substrate 210 to a predetermined thickness by spin-coating, thereby forming a second sacrificial layer 224, and the twice applied positive photoresist composition is exposed and developed. In such a manner, the sacrificial layer S having the first and second sacrificial layers 223 and 224 and having a planarized upper surface is formed in a space surrounded by the passage forming layer 220, as illustrated in FIG. 4A.

When forming the sacrificial layer S, an imide-based positive photoresist can be used as the positive photoresist, and blank exposure and development therefore do not need to be performed. In other words, if the imide-based positive photoresist is used as the positive photoresist, the height of the sacrificial layer S does not need to be made substantially equal to that of the passage forming layer 220. The imide-based positive photoresist should be subjected to hard baking at approximately 140° C. after being developed. However, the imide-based positive photoresist is not affected by a solvent contained in the negative photoresist composition and does not result in the generation of nitrogen gas even upon exposure, which will be described later in more detail.

As illustrated in FIG. 4B, a second negative photoresist layer 231 is formed on the substrate 210 having thereon the passage forming layer 220 and the sacrificial layer S. Since the second negative photoresist layer 231 forms a nozzle layer (see 230 of FIG. 4D), which will be described later, the second negative photoresist layer 231 should be chemically stable against ink. For this, the second negative photoresist layer 231 is formed to a predetermined thickness on the entire surface of the substrate 210 by a spin-coating process using a composition containing a prepolymer having a glycidyl ether functional group as described above. The second negative photoresist layer 231 can be formed as described above for the second negative photoresist layer 131.

As illustrated in FIGS. 4A and 4B, the sacrificial layer S can be formed to protrude higher than the passage forming layer 220. However, since the sacrificial layer S is formed of the imide-based positive photoresist, it is not affected by a solvent contained in the second negative photoresist layer 231, as described above. Thus, unlike in the prior art, the deformation or melting problem occurring at edges of the sacrificial layer S can be avoided.

Next, as illustrated in FIG. 4C, the second negative photoresist layer 231 can be exposed using a photomask 263 having a nozzle pattern. Subsequently, when the second negative photoresist layer 231 is developed, an unexposed portion of the second negative photoresist layer 231 is removed to form a nozzle 254, while the exposed and cured portion is left to form a nozzle layer 230, as illustrated in FIG. 4D.

Since the imide-based positive photoresist forming the sacrificial layer S does not produce nitrogen gas even upon exposure, the deformation problem of the nozzle layer 230 due to nitrogen gas in the prior art does not occur. Thus, radiation of an actinic ray can be used to expose the second negative photoresist layer 231. Specifically, a UV beam over a broadband, including I-line radiation (353 nm), H-line radiation (405 nm), and G-line radiation (436 nm), or e-beam or X-ray having wavelengths shorter than the broadband radiations, may be used.

As illustrated in FIG. 4E, an etch mask 271 can be formed on a rear surface of the substrate 210, and the substrate 210 exposed by the etch mask 271 is etched from the rear surface thereof to be perforated by dry etching or wet etching, thereby forming an ink supply hole 251. Specific steps for forming the etch mask 271 and the ink supply hole 251 are the same as those illustrated in FIGS. 3P-3Q.

Finally, the sacrificial layer S can be removed using a solvent, thereby forming an ink chamber 253 and a restrictor 252 surrounded by the passage forming layer 220 in a space obtained by the removal of the sacrificial layer S, as illustrated in FIG. 4F.

In such a manner, an inkjet printhead having the structure illustrated in FIG. 4F is completed. In embodiments, a step difference between the chamber layer of the inkjet printhead and the sacrificial layer is not greater than 3 μm.

FIGS. 6A through 6L are sectional views illustrating a method of manufacturing an inkjet printhead, including forming a passage forming layer and a nozzle layer using a negative photoresist composition including a prepolymer as described above and planarizing a sacrificial layer using a chemical mechanical polishing (CMP) process.

First, as illustrated in FIG. 6A, a heater 341 for heating ink and an electrode 342 for supplying current to the heater 341 are formed on a substrate 310. Here, a silicon wafer may be used as the substrate 310. The silicon wafer is widely used to manufacture semiconductor devices and is effective for mass production.

The heater 341 can be formed by depositing a resistive heating element, such as tantalum-nitride or a tantalum-aluminum alloy, on the substrate 310 by sputtering or chemical vapor deposition (CVD) and patterning the deposited resistive heating element. The electrode 342 can be formed by depositing a metal having good conductivity, such as aluminum or an aluminum alloy, on the substrate 310 by sputtering and patterning the deposited metal. Although not illustrated, a passivation layer made of silicon oxide or silicon nitride may be formed on the heater 341 and the electrode 342.

Next, as illustrated in FIG. 6B, a first negative photoresist layer 321 is formed on the substrate 310 having thereon the heater 341 and the electrode 342. The first negative photoresist layer 321 becomes a passage forming layer (see 320 of FIG. 6D) defining an ink passage including an ink chamber and a restrictor in a subsequent step as will be described later. The first negative photoresist layer 321 is crosslinked by radiation of actinic ray, such as UV light, and thus, is chemically stabilized against ink. The first negative photoresist layer 321 may be made of a composition containing a prepolymer having a glycidyl ether functional group on monomer repeating units as described above. In detail, the first negative photoresist layer 321 is formed by coating the composition to a predetermined thickness on the entire surface of the substrate 310. Here, the composition may be coated on the substrate using a spin coating process.

Next, as illustrated in FIG. 6C, the first negative photoresist layer 321 is exposed to UV light using a first photomask 361 having ink chamber and restrictor patterns. In the exposure step, a portion of the first negative photoresist layer 321 exposed to UV light is cured and thus develops a chemical resistance and a high mechanical strength. On the other hand, an unexposed portion of the first negative photoresist layer 321 is easily dissolved in a developer.

Next, when the first negative photoresist layer 321 is developed to remove the unexposed portion, as illustrated in FIG. 6D, a passage forming layer 320 defining an ink passage is formed.

Next, as illustrated in FIG. 6E, a sacrificial layer S is formed on the substrate 310 so as to cover the passage forming layer 320. Here, the sacrificial layer S is formed to have a higher height than the passage forming layer 320. The sacrificial layer S may be formed by coating a positive photoresist or a non-photosensitive soluble polymer to a predetermined thickness on the substrate 310 using a spin coating process. Here, the positive photoresist may be an imide-based positive photoresist. When the sacrificial layer S is made of an imide-based positive photoresist, it is hardly affected by a solvent, and does not generate a nitrogen gas upon exposure to light. Therefore, a process of hard baking the imide-based positive photoresist at a temperature of about 140° C. is required. Meanwhile, the sacrificial layer S may also be formed by coating a liquid non-photosensitive soluble polymer to a predetermined thickness on the substrate 310 using a spin coating process and baking the soluble polymer. Here, the soluble polymer may be at least one selected from the group consisting of a phenolic resin, a polyurethane resin, an epoxy resin, a polyimide resin, an acrylic resin, a polyamide resin, an urea resin, a melamine resin, and a silicon resin.

Next, as illustrated in FIG. 6F, upper surfaces of the passage forming layer 320 and the sacrificial layer S are planarized using a CMP process. In detail, when the upper surfaces of the sacrificial layer S and the passage forming layer 320 are polished by a CMP process to reach a desired height for the ink passage, the upper surfaces of the passage forming layer 320 and the sacrificial layer 160 are formed at substantially the same height.

Next, as illustrate in FIG. 6G a second negative photoresist layer 331 is formed on the passage forming layer 320 and the sacrificial layer S that have been planarized. The second negative photoresist layer 331 may be formed using a composition containing a prepolymer having a glycidyl ether functional group on monomer repeating units as described above, like the first negative photoresist layer 321. The second negative photoresist layer 331 becomes a nozzle layer (see 330 of FIG. 6I) in a subsequent process as will be described later. The second negative photoresist layer 331 is crosslinked by radiation of actinic ray, such as UV light, and thus, is chemically stabilized against ink. Specifically, the second negative photoresist layer 331 is formed by coating the composition to a predetermined thickness on the passage forming layer 320 and the sacrificial layer S using a spin coating process. Here, the second negative photoresist layer 331 is coated to have a thickness such that a sufficient nozzle length can be ensured and pressure variations in an ink chamber can be endured.

Moreover, since the sacrificial layer S and the passage forming layer 320 are planarized to have the same heights, transformation or melting of an edge portion of the sacrificial layer S, which may be caused due to reaction between the material forming the second negative photoresist layer 331 and the material forming the sacrificial layer S, does not occur. Therefore, the second photoresist layer 331 can be closely adhered to the upper surface of the passage forming layer 320.

Next, as illustrated in FIG. 6H, the second negative photoresist layer 331 is exposed using a second photomask 363 having a nozzle pattern. Then, when the second negative photoresist layer 331 is developed, an unexposed portion of the second negative photoresist layer 331 is removed to form a nozzle 354, and an exposed and cured portion of the second negative photoresist layer 331 is left to form a nozzle layer 330, as illustrated in FIG. 6I. Here, since the sacrificial layer S is made of an imide-based positive photoresist as described above, a nitrogen gas is not generated even though exposure-light reaches the sacrificial layer S beyond the second negative photoresist layer 331. Therefore, deformation of the nozzle layer 330 due to a nitrogen gas can be prevented.

Next, as illustrated in FIG. 6J, an etch mask 371 for forming an ink feed hole (see 351 of FIG. 6K) is formed on a rear surface of the substrate 310. The etch mask 371 may be formed by coating a positive or negative photoresist on the rear surface of the substrate 310 and patterning the photoresist.

Next, as illustrated in FIG. 6K, a rear surface of the substrate 310 exposed through the etch mask 371 is etched so as to penetrate the substrate 310 to thereby form an ink feed hole 351. Then, the etch mask 371 is removed. The etching of the rear surface of the substrate 310 may be performed by a dry etching process using plasma. Alternatively, the etching of the rear surface of the substrate 310 may also be performed by a wet etching process using tetramethylammonium hydroxide (TMAH) or KOH as an etchant.

Finally, when the sacrificial layer S is removed using a solvent, an ink chamber 353 and a restrictor 352 surrounded by the passage forming layer 320 are formed, and the electrode 342 for supplying current to the heater 341 is exposed, as illustrated in FIG. 6L. This completes an inkjet printhead having the structure illustrated in FIG. 6L.

EXAMPLES

Preparation of Resist Composition 1

50 ml xylene (commercially available from Samchun Chemical Co.) and 10 ml SP-172 (commercially available from Asashi Denka Korea Chemical Co.) were added to a reactor. 90 g of an epoxy resin in the trade name of EHPH-3150 (commercially available from Daicel Chemical Industries. Ltd.) was then added to the reactor, and the resultant solution was stirred for 24 hours.

Preparation of Resist Composition 2

A commercial resist solution of EPON SU-8 was obtained from MicroChem. Corp., and was used as received. The commercial solution included

-butyrolactone contained in an amount between 25 and 50% by weight, and a mixture of triarylsulfonium hexafluoroantimonate and p-thiophenoxyphenyldiphenysulfonium hexafluoroantimonate in propylene carbonate contained in an amount between 1 and 5% by weight.

Example 1

A tantalum nitride heater pattern and an electrode pattern made of AlSiCu alloy (the content of each of Si and Cu was 1% by weight or less) were each formed to a thickness of about 500 Å on a 6-inch silicon wafer using a sputtering process and a photolithography process commonly known in the art (see FIG. 3A).

Next, as illustrated in FIG. 3B, the resist composition 1 was spin-coated on the entire surface of the silicon wafer having thereon the heater pattern and the electrode pattern at a speed of 2000 rpm for 40 seconds and baked at 95° C. for seven minutes to form a first negative photoresist layer with a thickness of about 10 μm. Then, as illustrated in FIG. 3C, the first negative photoresist layer was exposed to UV light of I-line using a first photomask having predetermined ink chamber and restrictor patterns. At this time, the exposure dose was adjusted to 130 mJ/cm². Then, the wafer was baked at 95° C. for three minutes, dipped in a PGMEA developer for one minute for development, and rinsed with isopropanol for 20 seconds, to complete a passage forming layer pattern (see 120 of FIG. 3D).

An imide-based positive photoresist (trade name: PW-1270, manufactured by TORAY) was spin-coated on the entire surface of the wafer having thereon the passage forming layer pattern at a speed of 1000 rpm for 40 seconds, and baked at about 140° C. for 10 minutes to form a first sacrificial layer (see 123 of FIG. 3E). The thickness of the first sacrificial layer was adjusted such that the overcoat thickness of the first sacrificial layer on the passage forming layer pattern was about 5 μm.

The first sacrificial layer was exposed to UV light of I-line using a second photomask having predetermined pattern covering region between the passage forming layer pattern. At this time, the exposure dose was adjusted to 130 mJ/cm². Then, the wafer was baked at 95° C. for three minutes, dipped in a developer (AZ300K, manufactured by Clariant) for one minute for development, and rinsed with isopropanol for 20 seconds. This completed first sacrificial layer (see 123 of FIG. 3G).

An imide-based positive photoresist was spin-coated on the entire surface of the wafer having thereon the passage forming layer pattern and the first sacrificial layer, baked, exposed to light, baked (post-exposure bake), developed, and rinsed in the same manner as in the formation of the first sacrificial layer to form second sacrificial layer (see 124 of FIG. 3J). As a result, as illustrated in FIG. 3J, the sacrificial layer including the first sacrificial layer and the second sacrificial layer and having planarized upper surface was formed in space surrounded by the passage forming layer pattern.

Next, the sacrificial layers were subjected to blank exposure to UV light of 1-line at an exposure dose of 260 mJ/cm² such that the UV light reached a portion of the sacrificial layer that was the same level as the upper surface of the passage forming layer pattern. Then, the sacrificial layer was subjected to post-exposure bake, development, and rinsing to remove the exposed portion of the sacrificial layer so that the height of the sacrificial layer was equal to that of the passage forming layer pattern (see FIG. 3I).

A nozzle layer pattern was formed on the silicon wafer having thereon the passage forming layer pattern and the sacrificial layer using the resist composition 1 and a third photomask having a predetermined nozzle pattern under the same conditions as the formation of the passage forming layer pattern (see FIGS. 3N and 3O).

As illustrated in FIG. 3P, etch mask was formed on rear surface of the silicon wafer using a photolithography process commonly known in the art to form ink feed hole. Then, as illustrated in FIG. 3Q, the rear surface of the silicon wafer exposed through the etch mask was etched using a plasma etching process to form ink feed hole, and the etch mask was then removed. At this time, an etching power of a plasma etching apparatus was adjusted to 2000 Watt, an etching gas was a mixture gas of SF₆ and O₂ (mixture ratio: 10:1 by volume), and an etch rate was 3.7 μm/min.

Finally, the wafer was dipped in a methyl lactate solvent for two hours to remove the sacrificial layer, thereby forming ink chamber and restrictor surrounded by the passage forming layer pattern in space obtained by the removal of the sacrificial layer, as illustrated in FIG. 3R. This completed inkjet printhead having a structure as illustrated in FIG. 3R.

FIGS. 5A and 5B are vertical sectional views illustrating inkjet printhead manufactured according to the above-described method. Referring to FIGS. 5A and 5B, a cavity is not formed between a passage forming layer 120 and a nozzle layer 130, which suggests that the passage forming layer 120 and the nozzle layer 130 are firmly adhered to each other.

Example 2

This Example is intended to specifically describe a method of manufacturing an inkjet printhead, including forming a passage forming layer and a nozzle layer using a negative photoresist composition including a prepolymer as described above and planarizing a sacrificial layer using a CMP process.

A tantalum nitride heater pattern, an AlSiCu alloy electrode pattern, and a passage forming layer pattern were formed on a 6-inch silicon wafer in the same manner as in Example 1 (see FIGS. 6A through 6D).

Next, as illustrated in FIG. 6E, an imide-based positive photoresist was spin-coated on the entire surface of the wafer having thereon the passage forming layer pattern at a speed of 1000 rpm for 40 seconds, and baked at about 140° C. for 10 minutes to form sacrificial layer. The thickness of the sacrificial layer was adjusted such that the overcoat thickness of the sacrificial layer on the passage forming layer pattern was about 5 μm.

Next, upper surfaces of the passage forming layer pattern and the sacrificial layer were planarized using a CMP process, as illustrated in FIG. 6F. For this, the wafer was supplied onto a polishing pad (Model No.: JSR FP 8000, manufactured by JSR) of a polishing plate such that the sacrificial layer faced the polishing pad. Then, the wafer was pressed onto the polishing pad, under a pressure of 10−15 kPa with a backing pad, by a press head. While polishing slurries (FUJIMI Corporation, POLIPLA 103) were supplied onto the polishing pad, the press head was rotated with respect to the polishing plate. At this time, the rotation speed of each of the press head and the polishing pad was 40 rpm. The backing pad was made of a material whose Shore D hardness was 30˜70. The sacrificial layer was planarized at an etch rate of 5-7 μm/min until upper surface of the passage forming layer pattern was removed by a thickness of about 1 μm.

Images of the passage forming layer pattern and the sacrificial layer after the CMP process are shown in FIGS. 7A and 7B. Referring to FIGS. 7A and 7B, the upper surfaces of the passage forming layer pattern and the sacrificial layer were planarized by the CMP process.

Next, formation of the nozzle layer, formation of the ink feed hole, and removal of the sacrificial layer were performed in the same manner as in Example 1 except that the resist composition 2 was used as a nozzle layer forming composition, instead of the resist composition 1 to thereby complete inkjet printhead having a structure as illustrated in FIG. 6I.

FIGS. 8A and 8B are vertical sectional images of inkjet printhead manufactured as described in Example 2. Referring to FIGS. 8A and 8B, an ink chamber 353 and a restrictor 352 are formed to have substantially equal heights, and no cavity is generated between a passage forming layer 320 and a nozzle layer 330. Also, the nozzle layer 330 is firmly adhered to an upper surface of the passage forming layer 320.

As described above, since a upper surface of a sacrificial layer is planarized in methods of manufacturing an inkjet printhead according to various embodiments of the present general inventive concept, it is possible to overcome the deformation or melting problem occurring in the prior art, that is, it is possible to avoid the deformation or melting of edges of the sacrificial layer due to a reaction between a positive photoresist composition and a negative resist composition. Thus, a shape and dimension of an ink passage can be easily controlled, thereby improving a uniformity of the ink passage, ultimately improving ink ejection performance of the inkjet printhead. Also, since a passage forming layer and a nozzle layer are suitably adhered to each other, durability of the printhead is enhanced. Further, since nitrogen gas is not generated in the sacrificial layer during photography to form a nozzle, deformation of the nozzle layer due to nitrogen gas can be avoided. Accordingly, uniformity of the ink passage can be further enhanced.

Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents. 

1. A method of manufacturing an inkjet printhead, the method comprising: preparing a substrate having thereon a heater for heating ink and an electrode for supplying current to the heater; coating a negative photoresist composition on the substrate having thereon the heater and the electrode and patterning the negative photoresist composition using a photolithography process to form a passage forming layer that defines an ink passage; forming a sacrificial layer on the substrate having thereon the passage forming layer so as to cover the passage forming layer; planarizing upper surfaces of the passage forming layer and the sacrificial layer using a polishing process; coating a negative photoresist composition on the passage forming layer and the sacrificial layer and patterning the negative photoresist composition using a photolithography process to form a nozzle layer having a nozzle; forming an ink feed hole in the substrate; and removing the sacrificial layer, wherein the negative photoresist composition comprises a prepolymer that has a glycidyl ether functional group or a ring-opened glycidyl ether functional group on monomer repeating units thereof and a phenolic novolak resin-based backbone, a bisphenol A-based backbone, or an alicyclic-based backbone.
 2. The method of claim 1, wherein the polishing process is a chemical mechanical polishing (CMP) process.
 3. The method of claim 1, wherein the formation of the passage forming layer comprises: forming a first photoresist layer by coating the negative photoresist composition on the entire surface of the substrate; exposing the first photoresist layer using a first photomask having an ink passage pattern; and forming the passage forming layer by developing the first photoresist layer to remove an unexposed portion of the first photoresist layer.
 4. The method of claim 1, wherein the sacrificial layer comprises a positive photoresist or a non-photosensitive soluble polymer.
 5. The method of claim 4, wherein the positive photoresist is an imide-based positive photoresist.
 6. The method of claim 4, wherein the non-photosensitive soluble polymer is at least one selected from the group consisting of a phenolic resin, a polyurethane resin, an epoxy resin, a polyimide resin, an acrylic resin, a polyamide resin, an urea resin, a melamine resin, and a silicone resin.
 7. The method of claim 1, wherein in the formation of the sacrificial layer, the sacrificial layer is formed to be higher than the passage forming layer.
 8. The method of claim 1, wherein in the formation of the sacrificial layer, the sacrificial layer is formed using a spin coating process.
 9. The method of claim 1, wherein in the planariziation, the upper surfaces of the passage forming layer and the sacrificial layer are planarized by polishing the upper surfaces of the passage forming layer and the sacrificial layer using the polishing process to reach a desired height of the ink passage.
 10. The method of claim 1, wherein the formation of the nozzle layer comprises: forming a second photoresist layer by coating the negative photoresist composition on the passage forming layer and the sacrificial layer; exposing the second photoresist layer using a second photomask having a nozzle pattern; and forming the nozzle layer having the nozzle by developing the second photoresist layer to remove an unexposed portion of the second photoresist layer.
 11. The method of claim 1, wherein the formation of the ink feed hole comprises: coating a photoresist on a rear surface of the substrate; forming an etch mask for forming the ink feed hole by patterning the photoresist; and etching a rear surface portion of the substrate exposed through the etch mask to form the ink feed hole.
 12. The method of claim 11, wherein the rear surface of the substrate is etched by a dry etching process using plasma.
 13. The method of claim 11, wherein the rear surface of the substrate is etched by a wet etching process using tetramethylammonium hydroxide (TMAH) or KOH as an etchant.
 14. The method of claim 1, wherein the negative photoresist composition further comprises a cationic photoinitiator and a solvent.
 15. The method of claim 1, wherein the prepolymer is prepared from a backbone monomer unit selected from the group consisting of phenol, o-cresol, p-cresol, bisphenol-A, an alicyclic-based compound, and mixtures thereof.
 16. The method of claim 1, wherein the prepolymer comprises at least one represented by Formulae 1 through 7 below:

wherein m is an integer ranging from 1 to 25, and n is an integer ranging from 1 to
 20. 17. The method of claim 1, wherein the prepolymer comprises addition products of 1-2-epoxy-4(2-oxiranyl)-cyclohexane of 2,2-bis(hydroxy methyl)-1-butanol.
 18. The method of claim 1, wherein the prepolymer of the negative photoresist composition is crosslinked by exposure to radiation of actinic ray.
 19. The method of claim 14, wherein the cationic photoinitiator is a sulfonium salt or an iodonium salt.
 20. The method of claim 14, wherein the solvent is at least one selected from the group consisting of

-butyrolactone, propylene glycol methyl ether acetate (PGMEA), tetrahydrofuran (THF), methyl ethyl ketone, methy isobutyl ketone, cyclopentanone, and mixtures thereof.
 21. An inkjet printhead manufactured according to the method of any one of claims 1 through
 20. 